The MIMO transmission technique is a basic approach for exploiting and utilizing spatial dimension radio resources and improving utilization ratio of spectrum and utilization ratio of power, and it has been a mainstream technique researched and developed in the mobile communication field for more than a decade. Owing to the limitations of MIMO configuration of mobile terminals, the angle spread of MIMO channels at the base station is usually very small; in addition, owing to factors such as the existence of visible path, the performance of MIMO transmission links for single user usually suffers big limitation, and therefore it is difficult to fully exploit and utilize radio resources of spatial dimension. For this reason, multi-user MIMO or SDMA MIMO transmission technique on the same time-frequency resources has received attention; the SDMA MIMO technique can improve the utilization ratio of radio resources to a greater degree.
In SDMA MIMO systems, due to the asymmetry between uplink and downlink, the channels are classified into uplink multiple access channel (MAC) and downlink broadcast channel (BC). The research work is carried out in the two aspects, and mainly focuses on the downlink. In order to implement SDMA MIMO downlink transmission, it is required to use a pre-coding technique to eliminate or suppress the interference between users. Available SDMA pre-coding techniques include short-time pre-coding that utilizes short-time channel state information and long-time pre-coding that utilizes long-time channel state information; short-time pre-coding is applicable to fixed and low-speed mobile communication environments, while long-time pre-coding is applicable to middle or high speed mobile communication environments.
In actual systems, in order to obtain the channel state information required for coherent detection and channel measurement accurately and timely, usually a pilot symbol assisted channel estimation method is used. In the SDMA MIMO downlink, the number of orthogonal pilots and the quantity of time-frequency resources occupied by the orthogonal pilots for the channel estimation will increase as the number of base station antennae increases. One of the urgent tasks is how to carry out pilot and channel estimation for SDMA MIMO downlink on limited time-frequency resources. The present invention provides a pilot and channel estimation method for SDMA MIMO transmission downlink.